Implantable cardiac rhythm management system having multiple therapy modalities

ABSTRACT

A cardiac rhythm management system for providing a plurality of therapy modalities. For example, the system may include a cardiac resynchronization therapy module for providing cardiac resynchronization therapy and a pacemaker module for providing bradycardia therapy, as well as a selector module coupled to the cardiac resynchronization therapy module and the bradycardia module. The selector module may select an operating mode from among a plurality of operating modes including the cardiac resynchronization therapy module and the pacemaker module. Various manual and automatic methods may be used to select the operating mode. In addition, a reversion management system may be included to assist the cardiac rhythm management system to recover in case of a disruption to the system.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/460,975, filed Jun. 12, 2003, the specification of which is hereinincorporated by reference.

TECHNICAL FIELD

This invention relates to a cardiac rhythm management system. Inaddition, the invention relates to an implantable cardiac rhythmmanagement system having multiple therapy modalities. Further, theinvention relates to a cardiac rhythm management system including atleast bradycardia therapy and cardiac resynchronization therapycapabilities.

BACKGROUND

Numerous therapies have been developed to address the needs ofindividuals suffering from heart diseases or abnormalities. For a firstexample, individuals suffering from bradycardia, or an abnormally slowheart rate, can be treated using a pacemaker. A pacemaker alters theindividual's heart rate to return heart rate performance to normallevels. A pacemaker typically accomplishes this by delivering a seriesof electrical impulses to the heart tissue via one or more leads,thereby stimulating the heart tissue to contract at a specified rate.Therefore, a primary function of bradycardia therapy using a pacemakeris to provide rate support for the heart.

The pacemaker typically functions as an on-demand device, meaning thatthe pacemaker will function only when rate support is necessary. Thepacemaker will typically delay for a certain duration, termed an escapeinterval, before providing an electrical impulse to the heart. If theintrinsic electrical activity of the individual's heart causes the heartto contract before the escape interval expires, the pacemaker will notsend an electrical impulse. Instead, the pacemaker will reset the escapeinterval and wait for the escape interval to expire again. Therefore, ifthe individual's heart is beating at a specified acceptable rate, thepacemaker will not provide an electrical impulse until rate support isneeded. Other functions of a pacemaker may include adaptive-rate pacing,in which the rate of the pacing is increased or decreased based on anindividual's physiological needs.

In a second example of a heart abnormality, individuals may exhibit adecrease in hemodynamic efficiency due to the onset of congestive heartfailure (CHF). A possible therapy for CHF is the use of a cardiacresynchronization therapy (CRT) device. A CRT device, like a pacemaker,can deliver a series of electrical impulses to a heart tissue. However,a CRT device functions to synchronize the contraction of a heart ratherthan to pace the heart like a pacemaker. A CRT device may deliver aseries of electrical impulses to the heart at a set rate, usually inconjunction with each intrinsic heartbeat, to synchronize thecontraction of different sections of the heart. Research and developmentinto the use of a CRT device to treat CHF has established a set oftherapeutic features that can be customized for each individual in orderto maximize hemodynainic function. For instance, methods have beendeveloped for optimizing the timing between electrical stimuli, therebyproviding maximum resynchronization benefits. Therefore, a primaryfunction of a CRT device is resynchronization, making the timing and thedelivery of each electrical impulse for each heartbeat important.

Consequently, while bradycardia therapy focuses on rate support on anas-needed basis, CHF therapy focuses on resynchronization. Duringresynchronization, particular attention may be paid to atrioventriculardelays, and electrical impulses are typically provided for everyheartbeat. Because therapeutic priorities of bradycardia patients differfrom those of CHF patients, it is a current practice in the industry todesign different products for a patient depending on whether a patientexhibits bradycardia or CHF. Therefore, initial decisions must be madefor each patient on whether to implant a bradycardia pacemaker or a CHFcardiac resynchronization therapy device.

Currently, pacemakers and CRT devices are not interchangeable, and apacemaker cannot be reprogrammed to be a CRT device and vice versa.Therefore, not only must treatment decisions be made initially, once adevice is implanted into the patient, it cannot be adapted should thepatient's needs change, such as, for example, from a need forbradycardia therapy to a need for cardiac resynchronization therapy.Further, product development costs are increased because separatedevices must be designed.

It would therefore be desirable to develop a cardiac rhythm managementsystem having multiple therapy modalities.

SUMMARY

Generally, the present invention relates to a cardiac rhythm managementsystem. In addition, the invention relates to an implantable cardiacrhythm management system having multiple therapy modalities. Further,the invention relates to a cardiac rhythm management system including atleast bradycardia therapy and cardiac resynchronization therapycapabilities.

In one aspect, the invention relates to a cardiac rhythm managementsystem including a cardiac resynchronization therapy module forproviding cardiac resynchronization therapy, a pacemaker module forproviding bradycardia therapy, and a selector module coupled to thecardiac resynchronization therapy module and the pacemaker module,wherein the selector module selects an operating mode from among aplurality of operating modes including the cardiac resynchronizationtherapy module and the pacemaker module.

In another aspect, the invention relates to a method for a cardiacrhythm management system to select between a plurality of operatingmodes, the method including: detecting physiological data of anindividual; and selecting an operating mode from the plurality of modesfor the cardiac rhythm management system based on the physiologicalparameter.

In yet another aspect, the invention relates to a cardiac rhythmmanagement device including means for providing a first operating modeassociated with a first therapy for a heart, means for providing asecond operating mode associated with a second therapy for the heart,and means for selecting between the first operating mode and the secondoperating mode.

The above summary of the present invention is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The figures and the detailed description which follow moreparticularly exemplify these embodiments.

DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a schematic/block diagram illustrating one example embodimentof a cardiac rhythm management system coupled to a heart in accordancewith the present invention;

FIG. 2 is a graph showing atrial and ventricular depolarization as afunction of time;

FIG. 3 illustrates a plurality of modules associated with an examplecardiac rhythm management system made in accordance with the presentinvention;

FIG. 4 shows an operational flow of a cardiac rhythm management systemaccording to an embodiment of the present invention;

FIG. 5 illustrates an operational flow of a cardiac rhythm managementsystem in accordance with another embodiment of the present invention;

FIG. 6 shows an operational flow of a cardiac rhythm management systemaccording to an embodiment of the present invention;

FIG. 7 shows an operational flow of a reversion management subsystem ofa cardiac rhythm management system in accordance with another embodimentof the invention; and

FIG. 8 illustrates an operational flow of a cardiac rhythm managementsystem including a reversion management subsystem in accordance with anembodiment of the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION

The present invention relates to a cardiac rhythm management system. Inaddition, the invention relates to an implantable cardiac rhythmmanagement system having multiple therapy modalities. Further, theinvention relates to a cardiac rhythm management system including atleast bradycardia therapy and cardiac resynchronization therapycapabilities. While the present invention is not so limited, anappreciation of various aspects of the invention will be gained througha discussion of the examples provided below.

The present apparatus and methods are described with respect toimplantable cardiac rhythm management (CRM) systems, such as pacemakers,cardioverter/defibrillators, pacer/defibrillators, and multi-chamberand/or multi-site (in single or multiple heart chambers) cardiacresynchronization therapy (CRT) devices. Such CRT devices are includedwithin CRM systems even though the CRT devices need not necessarilymodulate heart rate. Such CRT devices may instead providecontraction-evoking stimulations that establish or modify the conductionpath of propagating depolarizations to obtain more efficient pumping ofthe heart. Moreover, the present apparatus and methods also findapplication in other implantable medical devices and in devices that maynot be implanted including, but not limited to, external pacemakers,cardioverter/defibrillators, pacer/defibrillators, multi-chamber and/ormulti-site CRT devices, monitors, programmers, and recorders, whethersuch devices are used for providing diagnostics, therapy, or both.

Example CRM systems and methods are described below. The systems andmethods provided are examples only, and other systems and methods canalso be used.

I. Example CRM System

A. Components of the CRM System

FIG. 1 is a schematic/block diagram illustrating one example embodimentof a CRM system 100 coupled to a heart 115. In this embodiment, system100 includes, among other components, a CRM device 105 that is coupledby leads 110A-B to the heart 115. The heart 115 includes four chambers:a right atrium 115A, a right ventricle 115B, a left atrium 115C, and aleft ventricle 115D. The heart 115 also includes a coronary sinus 115E,a vessel that extends from the right atrium 115A toward the leftventricular free wall.

In one embodiment, the lead 110A includes an electrode associated withthe right atrium 115A, such as tip electrode 120 and/or ring electrode125. The electrode is “associated” with the particular heart chamber byinserting it into that heart chamber, or by inserting it into a portionof the heart's vasculature that is close to that heart chamber, or byepicardially placing the electrode outside that heart chamber, or by anyother technique of configuring and situating an electrode for sensingsignals and/or providing therapy with respect to that heart chamber.Lead 110B, which is introduced into the coronary sinus 115E and/or thegreat cardiac vein or one of its tributaries, includes one or moreelectrodes associated with the left ventricle 115D, such as electrodes130 and 135. The device 105 may also include other electrodes, such ashousing electrode 150 and/or header electrode 155, which are useful for,among other things, unipolar sensing of heart signals or unipolardelivery of contraction-evoking stimulations in conjunction with one ormore of the electrodes 120, 125, 130, and 135 associated with the heart115. Alternatively, bipolar sensing and/or therapy may be used betweenelectrodes 120 and 125, between electrodes 130 and 135, or between oneof electrodes 130 and 135 and another closely situated electrode.

The CRM device 105 includes a sensing module 160 that is coupled to oneor more of the electrodes for sensing electrical depolarizationscorresponding to heart chamber contractions. Such electricaldepolarizations of the heart tissue include atrial depolarizations,referred to as P-waves, and ventricular depolarizations, referred to asQRS complexes. The QRS complex is a rapid sequence of several signalexcursions away from a baseline in sequentially switching polarity, withthe largest excursion referred to as an R-wave. See FIG. 2, showing agraph of atrial and ventricular depolarizations.

A peak detector 165 is coupled to sensing module 160 for detecting theP-wave peak from the right atrium 115A, obtained by bipolar sensingbetween electrodes 120 and 125 or by any other sensing technique. Thepeak detector 165 also senses the R-wave peak at a plurality ofdifferent sites associated with the left ventricle 115D, such as at eachof the electrodes 130 and 135. In one example, the electrode 130 islocated near the left ventricular apex and the electrode 135 is locatednear the left ventricular base regions, i.e., closer to the left atrium115C.

In another example, one of the two electrodes 130 and 135 (or anadditional third electrode) is located in a middle portion (“midregion”)of the left ventricle 115D between the left ventricular apex and theleft ventricular base region. In another example, the electrodes 130 and135 are located in a middle cardiac vein closer to a wall of theventricle. Sensing at the electrodes 130 and 135 is either unipolar(e.g., the electrode 130 and/or 135 is sensed in combination with arelatively distant electrode, such as one or both of housing electrode150 and/or header electrode 155) or bipolar (e.g., the electrode 130and/or 135 is sensed in combination with another relatively closeelectrode, such as another electrode disposed on the lead 110B andassociated with the left ventricle 115D, or another electrode disposedon the lead 110A and associated with the right atrium 115A).

The system 100 may also include a telemetry transceiver 185 disposed inthe device 105, which is communicatively coupled to an externalprogrammer 190. A time module 170 may also be included to measure a timeduration between various events, such as, for example, the duration oftime between adjacent contractions of the heart 115.

The system 100 includes multiple therapy modalities. For example, asdiscussed below, the system 100 may provide both bradyeardia therapy(“pacemaker mode”), as well as cardiac resynchronization therapy (“CRTmode”). The mode in which the system 100 is currently operating istermed the “operating mode.” Although the example embodiments illustratetwo therapy modalities, other therapy modalities may also be provided.

A controller 175 is provided to select an operating mode from among themultiple therapy modalities. The controller 175 may select the operatingmode using one or more of the methods described below. Once selected,the controller 175 communicates the operating mode to a therapy module180.

The therapy module 180 is coupled to electrodes 130 and 135 for deliveryof a desired therapy modality, specifically the therapy modalityassociated with the selected operating mode, to the heart 115. Thetherapy module 180 is configured to deliver the desired therapy modalityusing a plurality of operating parameters, as described below.

B. Reuse of OperatingZ Parameters

The operating mode for the system may be selected using both automaticand manual methods, as disclosed below. Correct selection of theoperating mode can be important for several reasons, including thatoperating parameters associated with the different operating modes, aswell as the goals of the therapies associated with each operating mode,may differ significantly. An “operating parameter” is a configurationvariable associated with a specific aspect of a given therapycontrolling how the CRM device functions. For example, an operatingparameter may include a stimulation and sensing configuration such as“VDD,” which is a standard industry convention for cardiac rhythmmanagement systems. See, e.g., U.S. Pat. No. 5,792,203 to Schroeppel.Although the two example therapy modalities provided in the embodimentdisclosed herein share some of the same operating parameters and areimplemented as a single system, differences exist.

For example, Table 1 provided below illustrates some of the differencesfor several operating parameters associated with pacemakers and CRTdevices, as are well known to those of ordinary skill in the art.

TABLE 1 Typical Operating Parameters Associated with Example OperatingModes CHF - Parameter Bradycardia - Pacemaker CRT DeviceStimulation/Sensing Mode DDD(R) VDD LRL 60 ppm 40 ppm Noise Response DOOinhibit Atrioventricular Delay 120 ms 100 ms

As Table 1 illustrates, the operating parameters associated withdifferent therapies may vary significantly. For example, if the deviceis operating in CRT mode, the device may include operating parametersrequiring the device to inhibit the delivery of electrical impulses(i.e., Noise Response=inhibit) if interference causes the device to loseatrial sensing, rather than to deliver electrical impulsesasynchronously, as this may decrease hemodynamic performance. On theother hand, if the device is operating in pacemaker mode, the device mayinclude operating parameters requiring the device to continue to deliverelectrical impulses (i.e., Noise Response=“DOO” mode) asynchronously.Because selection of the incorrect operating mode can actually decreasehemodynamic performance, it is important to correctly determine whichtherapy is appropriate for each patient.

Whenever possible, operating parameters that are common between a CRTmode and a pacemaker mode are shared. As shown in FIG. 3, the examplecontroller 175 and therapy module 180 are illustrated in greater detail.The therapy module 180 includes a pacemaker module 335, a CRT module340, and operating parameters 311-317 associated with the modules 335and 340. The controller 175 includes an operating mode selector module355 coupled to the modules 335 and 340, as well as a protected memorymodule 360 and a detector module 370, both coupled to the operating modeselector module 355.

The pacemaker module 335 in this example embodiment is associated withthe plurality of operating parameters 311-314. The CRT module 340includes the plurality of operating parameters 314-317. The operatingparameter 314 is common to both the pacemaker module 335 and the CRTmodule 340 and therefore is shared. However, other operating parametersthat are not common between the two modules 335 and 340 are maintainedseparately to avoid conflicts. For example, the operating parametersprovided in Table 1 differ and therefore are not shared between thedifferent modes. Further, other operating parameters may be specific toone mode and therefore would not be shared. For example, operatingparameters associated with implementing hysterisis may be relevant forpacemaker mode but may not be relevant for CRT mode requiringstimulation at regular intervals. However, other parameters, such asstimulation amplitude and width, P- and R-wave sensing sensitivity,antitachycardia response parameters, etc., may be common to both modes.

C. Configuration of the CRM System

The therapy module 180 of FIG. 3 is further divided into twohierarchical program levels to illustrate the programmable capabilitiesof the cardiac rhythm management system 100. Additionally illustrated inFIG. 3 are lower program level 310 and higher program level 330. Inorder to manually program the system 100, a caregiver may utilizeoperating mode selector module 355 to select between pacemaker module335 and CRT module 340. Because this selection is made in the higherprogram level 330, the caregiver is allowed to simply select between thetwo modes, and the system 100 automatically uses nominal operatingparameters associated with either the pacemaker mode or the CRT mode.For example, if the operating mode selector module 355 is utilized toselect pacemaker mode, the associated nominal operating parameters311-314 are utilized to configure the pacemaker module 335.

However, in some patients the nominal operating parameters will not besufficient to provide optimal hemodynamic benefits. In these cases, thecaregiver may further configure the individual operating parametersassociated with an operating mode. These modifications are made in thelower program level 310, in which specific operating parametersassociated with the modules 335 and 340 may be configured. For example,if the caregiver utilizes the operating mode selector module 355 toselect the pacemaker module 335, the caregiver can configure operatingparameters 311-314 to further tailor the pacemaker module 335 tomaximize hemodynamic benefits. In this manner, the system 100 mayprovide ease of use by allowing for selection between the pacemakermodule 335 and the CRT module 340 in the higher program level 330, aswell as provide for added configurability by allowing for themodification of parameters 311-317 in the lower program level 310.

The operating mode selector module 355 of the controller 175 may furtherutilize the detector module 370 to automatically select betweenoperating modes. The detector module 370 provides the operating modeselector module 355 with physiological data necessary to implement oneor more of the methods described below to automatically select betweenthe two example operating modes. This physiological data may becollected from the patient manually or automatically by the system.

II. Example Methods Used to Select Between the Multiple TherapyModalities

Selection between the multiple therapy modalities may be automatic ormanual. Both automatic (i.e., can be performed by the system 100 withoutmanual intervention) and manual methods for selection of the operatingmode are similar in that both may compare a patient's hemodynamicresponse when operating in various therapy modalities. For example, oneor more methods may be used to determine whether the CRM deviceoperating in a first operating mode achieves a better hemodynamicresponse than when operating in a second operating mode.

For example, in the example method illustrated in FIG. 4, adetermination is made as to whether the application of cardiacresynchronization therapy would be beneficial to the patient, as shownin operation 410. If the application of cardiac resynchronizationtherapy would result in the same or an increase in hemodynamicperformance, control is passed to operation 440, and the CRM device isplaced in CRT mode. Alternatively, if the application of cardiacresynchronization therapy would result in a decrease in hemodynamicperformance, then control is passed to operation 430 and the CRM deviceis placed in pacemaker mode. All of the methods described below forselecting between the two example modes may implement, at some level,the method as shown in FIG. 4.

In FIG. 5, an example high-level operational flow 500 is provided for acardiac rhythm management system such as 100. At operation 510, thesystem is implanted into a patient using known techniques. Inconjunction with, or possibly after implantation, control is passed tooperation 520, where a determination is made as to the appropriatetherapy to provide to the patient. In the example embodiment, theoperation 520 selects between multiple therapy modalities that may bedelivered to the patient for treatment of an arrhythmic condition.

In the illustrated method, the therapies include bradycardia therapy(pacemaker mode) and cardiac resynchronization therapy (CRT mode),although other therapies may also be provided. In addition, within eachtherapy modalities (i.e., the pacemaker mode and the CRT mode), aplurality of sub-therapy modalities can be provided such as, forexample, multiple therapies that can be administered to remedybradycardia.

Selection of the appropriate therapy modality can be achieved manually,using, for example, the external programmer 190 (see, e.g., FIG. 1).Alternatively, the controller 175 may automatically select betweenpacemaker mode and CRT mode using one or more of the methods describedbelow.

If the therapy modality selected is pacemaker mode, control is passed tooperation 530 and the system functions as a state of the art pacemakerwith all associated modalities. Alternatively, if the CRT mode isselected, control is passed to operation 540, and the system functionsas a state of the art CRT device.

A variety of methods may be used to make the selection in operation 520,as described below.

A. Q*S* Method

In U.S. patent application Ser. No. 10/008,397, filed on Dec. 6, 2001and entitled “IDENTIFYING HEART FAILURE PATIENTS SUITABLE FORRESYNCHRONIZATION THERAPY USING QRS COMPLEX WIDTH FROM AN INTRACARDIACELECTROGRAM,” incorporated by reference herein in its entirety, a methodis described for identifying patients who may benefit from cardiacresynchronization therapy through analysis of the duration ofventricular depolarization, or the width of the QRS complex, measuredintracardially. According to the method, an intracardiac electrogram isdigitalized and smoothed using a rectangular moving window. The time ofpeak depolarization (R) is determined and the absolute derivative of thewaveform is calculated. Next, the maximum absolute derivative before R(“max-BR”) and after R (“max-AR”) are determined. The Q* point is thefirst point before R at which the absolute derivative is approximately2% of max-BR, and the S* is the first point after R at which theabsolute derivate is approximately 10% of max-AR, The Q*S* interval isthen compared to a threshold value. If the duration is greater than orequal to the threshold, the patient is labeled a responder to cardiacresynchronization therapy and, in operation 520, CRT mode is selected.Alternatively, if the duration is less than the threshold, pacemakermode may be used. In one embodiment of the method, the threshold is setat approximately 170 milliseconds. Other durations, as well as otherthreshold values, may also be used.

B. Interval between Q-wave−LV (lead) Method

Another method that may be employed to select an operating mode for theCRM device includes measurement of a duration of the onset ofventricular depolarization measured from either a surface ECG or leftventricular intracardiac electrogram to the peak of the left-ventricularintracardiac electrogram at the stimulation site (the “Q-wave-LVinterval”). This Q-wave-LV interval is measured, and the duration iscompared to a threshold value. If the duration is greater than or equalto the threshold, the stimulation site is labeled a responder site tocardiac resynchronization therapy and CRT mode is selected.Alternatively, if the duration is less than the threshold, pacemakermode may be used. In one embodiment of the method, the threshold is setat approximately 80 milliseconds if Q is measured from a surface ECG and100 milliseconds if Q is measured intracardially. Other threshold valuesmay also be used.

C. Surface QRS Wave Method

Another method that may be employed to select an operating mode for theCRM device includes measurement of a duration of ventriculardepolarization, or the QRS complex, at the surface of the patient (i.e.,intercardially) and comparison of that duration to a threshold value. Ifthe duration is greater than or equal to the threshold, the patient islabeled a responder to cardiac resynchronization therapy and CRT mode isselected. Alternatively, if the duration is less than the threshold,pacemaker mode may be used. In one embodiment of the method, thethreshold is set at approximately 150 milliseconds. Other thresholdvalues may also be used.

D. Interventricular Pressure Method

Another method that may be employed to determine a correct operatingmode for the system is generally described in U.S. Pat. No. 6,280,389 toDing et al., incorporated by reference herein in its entirety. Thismethod involves measurement of a patient's left and right ventricularpressure for a specified period of time using a pressure-measuringdevice. A normalized pressure loop area for each heartbeat measured isthen calculated and a mean pressure area determined. This mean pressurearea is then compared to a threshold value to determine whether thepatient is a responder. If the area is equal to or greater than thethreshold, the patient is labeled a responder, and CRT mode is selected.Alternatively, if the area is less than the threshold, pacemaker mode isselected. In an example disclosed in the patent, the threshold is set to0.3.

E. Paced QRS Method

Another method that may be employed to determine a correct operatingmode for a CRM system is generally described in U.S. patent applicationSer. No. 09/822,790, filed on Mar. 30, 2001 and entitled “METHOD ANDAPPARATUS FOR PREDICTING ACUTE RESPONSE TO CARDIAC RESYNCHRONIZATIONTHERAPY,” incorporated by reference herein in its entirety. The methodgenerally described in this application involves measuring a firstinterval during an intrinsic systolic cycle, measuring a second intervalduring a stimulation-induced systolic cycle, and comparing a percentagechange in duration between the first interval and the second intervalagainst a pre-determined threshold. The interval disclosed is apatient's intrinsic ventricular depolarization, although other intervalsmay also be used. If the percentage change is equal to or less than thethreshold, disclosed as between 10-25 percent, then the patient may belabeled a “responder” and the CRM device may be set to perform in CRTmode. Alternatively, if the percentage change is greater than 10-25percent, then the CRM device may be set to perform in pacemaker mode.

As previously indicated, the determination made in operation 420 may beautomatically made by a CRM system using one or more of the methodsdescribed above, or other similar methods. Further, the operating modemay be manually selected by a caregiver and the CRM system manuallyprogrammed.

F. Automatic Reconfiguration Method

A method 600 according to another embodiment of the invention isillustrated in FIG. 6. The method 600 is similar to the method 500illustrated in FIG. 5, except that once the operating mode has beenselected by operation 620, control is periodically passed back tooperation 620 to make a new determination of the correct operating mode.The device may be set to make this new determination at certainintervals, such as daily or weekly, or the device may be set to makethis new determination after a certain event has occurred, such as thefailure to sense an intrinsic wave (e.g., an R-wave) after a giveninterval. In this manner, a CRM system implementing the method 600periodically reevaluates and adapts to a patient's needs as thepatient's needs change. For example, a patient receiving bradycardiapacing support may develop a need for CRT therapy as the patient's needschange. In method 600, the CRM system may automatically detect thischange in the patient's needs and switch from pacemaker mode to CRT modeor vice versa.

III. Example Reversion Management System

Another aspect of the invention is a reversion management system. Thereversion management system generally includes a protected memory module360, shown in FIG. 3, to store one or more operating parametersassociated with an operating mode. The one or more operating parametersstored in the protected memory module 360 are collectively referred toherein as a reversion mode. During typical CRM system operation, severaldifferent environmental conditions may disrupt normal CRM systemperformance. Such conditions may include high power antennas for radiobroadcasting, anti-theft devices used in convenience stores entrances,electrosurgery conducted on the patient, or other such electrical ormagnetic interference that may disrupt normal operation. The reversionmode provides the necessary operating parameters associated with thecorrect operating mode should normal device operation be disrupted.

The protected memory module 360 is a protected memory space based on aspecialized hardware design. Typically, an 8-bit memory has a 3-bitparity check associated with it, so that any of the 8-bits can berestored if corrupted. Hamming error correction may also be used toensure that the memory module 360 is free from corruption.

A method 700 illustrated in FIG. 7 shows an example operational flow forthe reversion management system. In operation 710, a CRM systemdetermines whether it is currently operating in pacemaker mode or CRTmode. If the CRM device determines that the operating mode is pacemakermode, control is passed to operation 720, and the operating parametersassociated with the pacemaker mode are stored in a protected memorymodule. Alternatively, if the CRM device determines that the currentoperating mode is CRT mode, control is passed to operation 730, and theoperating parameters associated with the CRT mode are stored in theprotected memory module. The reversion mode stored in the protectedmemory module may be updated periodically, such as daily or weekly, sothat the most current operating parameters associated with the operatingmode are stored in the protected memory module.

The operating parameters stored in the protected memory module may benominal operating parameters associated with a typical pacemaker or CRTdevice, or may be the actual parameters associated with an operatingmode. For example, nominal operating parameters for a pacemaker mode maybe sufficient for most patients exhibiting bradycardia because of therather homogeneous clinical indications associated with bradycardia.Therefore, nominal values may, but need not, be stored in the protectedmemory as the reversion mode if the device is operating in pacemakermode. On the other hand, CRT patients typically are not homogenous andtherefore require operating parameters adapted individually for eachpatient. Therefore, actual operating parameters associated with the CRTmode may be stored in the protected memory as the reversion mode.

An example operational flow 800 shown in FIG. 8 illustrates how a CRMdevice may utilize a reversion mode stored in a protected memory torecover from a disruption. In operation 810, the CRM device isfunctioning normally in an operating mode. In 820, a disruption to theCRM device occurs, such as from one of the external conditions describedabove. After the CRM device recovers from the disruption, in operation825 the CRM device determines whether a reversion mode has been storedin the protected memory. If no reversion mode has been stored inprotected memory, control is passed to operation 826 and nominaloperating parameters are used. However, if a reversion mode has beenstored, control is passed to operation 830 and the CRM device accessesthe reversion mode stored in the protected memory. Finally, in operation840, the CRM device resets the operating mode based on the reversionmode to allow the CRM device to function in a manner similar to thatbefore the disruption.

Therefore, in this manner, the CRM device may recover from a disruptionand continue to provide beneficial therapy to the patient. The reversionmode allows the CRM device to use the correct operating parameters andcontinue to operate correctly after a disruption to the CRM deviceoccurs.

The embodiments of the invention described herein may exhibit severaladvantages over prior devices. The CRM systems disclosed herein providea plurality of therapy modalities, rather than a single therapy. In thismanner, costs associated with product development are reduced. Further,because the CRM system may be reprogrammed while ambulatory to providedifferent therapies, the device may adapt to a patient's needs as thepatient's needs change over time. In addition, because the device isreprogrammable, operating parameters associated with the operating modemay be tailored to provide optimal hemodynamic benefits. Also, a CRMdevice implemented according to the invention may automatically selectthe operating mode and thereby reduce or eliminate errors made by acaregiver in the selection of an appropriate operating mode and maycontinue to provide optimal therapy to the patient even after recoveryfrom a disruption.

The methods of the present disclosure can be implemented using a systemas shown in the various figures disclosed herein comprising variousdevices and/or programmers, including implantable or external devices.Accordingly, the methods of the present disclosure can be implemented:(1) as a sequence of computer implemented steps running on the system;and (2) as interconnected modules within the system. The implementationis a matter of choice dependent on the performance requirements of thesystem implementing the method of the present disclosure and thecomponents selected by or utilized by the users of the method.Accordingly, the logical operations making up the embodiments of themethod of the present disclosure described herein can be referred tovariously as operations, steps, or modules. It will be recognized by oneof ordinary skill in the art that the operations, steps, and modules maybe implemented in software, in firmware, in special purpose digitallogic, analog circuits, and any combination thereof without deviatingfrom the spirit and scope of the present invention as recited within theclaims attached hereto.

The present invention should not be considered limited to the particularexamples described above, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention may be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification.

1. A cardiac rhythm management system comprising: a cardiacresynchronization therapy module for providing cardiac resynchronizationtherapy; a pacemaker module for providing bradycardia therapy; sensingcircuitry to collect electrophysiological data indicating the presenceor absence of a ventricular conduction delay; a selector module coupledto the cardiac resynchronization therapy module and the pacemakermodule, wherein the selector module is configured to select an operatingmode from among a plurality of operating modes including the cardiacresynchronization therapy module and the pacemaker module; means formeasuring ventricular pressure in at least one ventricle; and, whereinthe selector module is configured to automatically select between thecardiac resynchronization therapy module and the pacemaker module basedupon the collected electrophysiological data indicating the presence orabsence of a ventricular conduction delay and ventricular pressuremeasurement.
 2. The system of claim 1, wherein the selector module isconfigured to automatically select between the cardiac resynchronizationtherapy module and the pacemaker module on a continuous basis.
 3. Thesystem of claim 1, wherein the selector module is further configured tocompare an interval between a beginning of an intrinsic ventriculardepolarization designated as Q* and an ending of the intrinsicventricular depolarization designated as S* to a threshold in order toautomatically select between the cardiac resynchronization therapymodule and the pacemaker module.
 4. The system of claim 1, wherein theselector module is configured to automatically select between thecardiac resynchronization therapy module and the pacemaker module on aperiodic basis.
 5. The system of claim 1, wherein the selector module isfurther configured to: detect a time of peak depolarization R in anelectrogram waveform; derive an interval between a beginning of anintrinsic ventricular depolarization designated as Q* as the point atwhich a derivative of the electrogram waveform exceeds a specifiedpercentage of the maximum derivative of the electrogram waveform beforeR; derive an ending of the intrinsic ventricular depolarizationdesignated as S* as the point at which a derivative of the electrogramwaveform exceeds a specified percentage of the maximum derivative of theelectrogram waveform after the depolarization peak; and, compare Q* andS* to a threshold in order to automatically select between the cardiacresynchronization therapy module and the pacemaker module.
 6. The systemof claim 1, further comprising a protected memory module coupled to theselector module, wherein a plurality of operating parameters associatedwith the operating mode are stored in the protected memory module at aperiodic interval.
 7. The system of claim 1, further comprising: meansfor storing a plurality of operating parameters associated with theoperating mode in a protected memory at a periodic interval; and meansfor accessing the plurality of parameters upon disruption of the cardiacrhythm management system.
 8. The system of claim 1, further comprising:means for measuring a first point of an onset of ventriculardepolarization; means for measuring a second point of a peak of aleft-ventricular intracardiac electrogram; means for calculating aninterval based on the first and second points; and means for comparingthe interval to a threshold to select the operating mode.
 9. The systemof claim 1, wherein the ventricular pressure means comprises means formeasuring pulse pressures in both a right ventricle and a left ventricleand further comprising: means for calculating a normalized pressure looparea based on the pulse pressures; and means for comparing thenormalized pressure loop area to a threshold to select the operatingmode.
 10. The system of claim 1, wherein an AV delay used for cardiacresynchronization therapy is shorter than the AV delay used forbradycardia therapy.
 11. A method for operating a cardiac rhythmmanagement system, comprising: selectably providing either cardiacresynchronization therapy via a cardiac resynchronization therapy moduleor bradycardia therapy via a pacemaker module; collectingelectrophysiological data indicating the presence or absence of aventricular conduction delay; measuring ventricular pressure in at leastone ventricle selecting between the cardiac resynchronization therapymodule and the pacemaker module based upon the collectedelectrophysiological data indicating the presence or absence of aventricular conduction delay and ventricular pressure measurement. 12.The method of claim 11, further comprising selecting between the cardiacresynchronization therapy module and the pacemaker module on acontinuous basis.
 13. The method of claim 11, further comprisingcomparing an interval between a beginning of an intrinsic ventriculardepolarization designated as Q* and an ending of the intrinsicventricular depolarization designated as S* to a threshold in order toautomatically select between the cardiac resynchronization therapymodule and the pacemaker module.
 14. The method of claim 11, furthercomprising selecting between the cardiac resynchronization therapymodule and the pacemaker module on a periodic basis.
 15. The method ofclaim 11, further comprising: detecting a time of peak depolarization Rin an electrogram waveform; deriving an interval between a beginning ofan intrinsic ventricular depolarization designated as Q* as the point atwhich a derivative of the electrogram waveform exceeds a specifiedpercentage of the maximum derivative of the electrogram waveform beforeR; deriving an ending of the intrinsic ventricular depolarizationdesignated as S* as the point at which a derivative of the electrogramwaveform exceeds a specified percentage of the maximum derivative of theelectrogram waveform after the depolarization peak; and, comparing Q*and S* to a threshold in order to automatically select between thecardiac resynchronization therapy module and the pacemaker module. 16.The method of claim 11, further comprising storing a plurality ofoperating parameters associated with the operating mode in a protectedmemory module at a periodic interval.
 17. The method of claim 11,further comprising: storing a plurality of operating parametersassociated with the operating mode in a protected memory at a periodicinterval; and accessing the plurality of parameters upon disruption ofthe cardiac rhythm management system.
 18. The method of claim 11,further comprising: measuring a first point of an onset of ventriculardepolarization; measuring a second point of a peak of a left-ventricularintracardiac electrogram; calculating an interval based on the first andsecond points; and comparing the interval to a threshold to select theoperating mode.
 19. The method of claim 11, further comprising:measuring pulse pressures in both a right ventricle and a leftventricle; calculating a normalized pressure loop area based on thepulse pressures; and comparing the normalized pressure loop area to athreshold to select the operating mode.
 20. The method of claim 11,wherein an AV delay used for cardiac resynchronization therapy isshorter than the AV delay used for bradycardia therapy,